This invention relates to producing shale oil by mining a subterranean deposit of oil shale. More particularly it relates to an improved process for disposing of the spent mineral materials which are left by the retorting or pyrolyzing of the oil shale to produce the shale oil.
Various procedures have been suggested for replacing spent oil shale materials in the voids formed within the subterranean oil shale deposit. For example, U.S. Pat. No. 3,340,693 suggests mining oil shale and backfilling at least some of the mined out spaces with porous masses of particles through which a suitable reagent is flowed to consolidate the masses. U.S. Pat. No. 3,459,003 suggests mining and retorting oil shale, pumping a slurry containing some of the spent shale into the mine to form a porous mass, thermally converting the remainder of the spent shale to a cement, and pumping a slurry of the cement into the mine to fill the pores of the porous mass of spent shale. U.S. Pat. No. 3,588,175 suggests dividing a zone being mined into a number of production levels, mining concurrently on several levels while leaving relatively weak pillars between adjacent stopes, then promptly providing bulkheads and pumping slurries of spent shale into the emptied stopes while removing water to allow the spent shale masses to compact under their own weight.
The National Technical Information Service PB-254 728, Feb. 20, 1976, on Field Compaction Tests, Research and Development Program on the Disposal of Retorted Oil Shale-Paraho Oil Shale Project, describes compaction characteristics of the spent shale relative to treatments with various types and techniques used for road beds or dams, compacting devices such as sheepsfoot or rubber tire rollers, vibratory pads, tractors, or the like. The report indicates that the densities of the compacted spent shales were about 1.5 gm/cc. Such compactions leave about a 20% excess of bulk volumes relative to the bulk volumes of the subterranean oil shale from which the spent shales were obtained.